Weak anti-localization in undoped Ge/GeSn heterostructures*

In this work, we demonstrate weak anti-localization (WAL) in undoped Ge/GeSn heterostructures. We used gated Hall-bar devices to induce two-dimensional hole gases (2DHGs) in strained GeSn quantum wells for magnetotransport experiment at 1.2 to 10 K. Transition from weak localization to WAL is observed as the density increases due to density dependent spin-orbit coupling. By fitting to the HLN formula, phase coherence and spin-orbit times of 2DHGs as well as the spin-orbit splitting energy in undoped Ge/GeSn heterostructures are extracted. Our data show that the scattering lifetime is shorter than the spin-orbit time at all densities, indicating that the system is in the spin-diffusive regime.